Spatio-temporal analysis on enterovirus cases through integrated surveillance in Taiwan

Ta-Chien Chan,Rung-Hung Chen,Jing-Shiang Hwang,Chwan-Chuen King,Po-Huang Chiang

doi:10.1186/1471-2458-14-11

Abstract

BackgroundSevere epidemics of enterovirus have occurred frequently in Malaysia, Singapore, Taiwan, Cambodia, and China, involving cases of pulmonary edema, hemorrhage and encephalitis, and an effective vaccine has not been available. The specific aim of this study was to understand the epidemiological characteristics of mild and severe enterovirus cases through integrated surveillance data.MethodsAll enterovirus cases in Taiwan over almost ten years from three main databases, including national notifiable diseases surveillance, sentinel physician surveillance and laboratory surveillance programs from July 1, 1999 to December 31, 2008 were analyzed. The Pearson’s correlation coefficient was applied for measuring the consistency of the trends in the cases between different surveillance systems. Cross correlation analysis in a time series model was applied for examining the capability to predict severe enterovirus infections. Poisson temporal, spatial and space-time scan statistics were used for identifying the most likely clusters of severe enterovirus outbreaks. The directional distribution method with two standard deviations of ellipse was applied to measure the size and the movement of the epidemic.ResultsThe secular trend showed that the number of severe EV cases peaked in 2008, and the number of mild EV cases was significantly correlated with that of severe ones occurring in the same week [r = 0.553, p < 0.01]. These severe EV cases showed significantly higher association with the weekly positive isolation rates of EV-71 than the mild cases [severe: 0.498, p < 0.01 vs. mild: 0.278, p < 0.01]. In a time series model, the increase of mild EV cases was the significant predictor for the occurrence of severe EV cases. The directional distribution showed that both the mild and severe EV cases spread extensively during the peak. Before the detected spatio-temporal clusters in June 2008, the mild cases had begun to rise since May 2008, and the outbreak spread from south to north.ConclusionsLocal public health professionals can monitor the temporal and spatial trends plus spatio-temporal clusters and isolation rate of EV-71 in mild and severe EV cases in a community when virus transmission is high, to provide early warning signals and to prevent subsequent severe epidemics.

Highlights

Severe epidemics of enterovirus have occurred frequently in Malaysia, Singapore, Taiwan, Cambodia, and China, involving cases of pulmonary edema, hemorrhage and encephalitis, and an effective vaccine has not been available
The question is, what are the important epidemiological characteristics that will be helpful in surveillance of EV-71 to minimize the severity of future epidemics? The specific aims of this study were: (1) to elucidate the spatio-temporal correlations between the mild and severe enterovirus cases through integrating the data of the three enterovirusrelated surveillance systems, including the sentinel physician, national notifiable diseases and laboratory surveillance systems in Taiwan, (2) to find out the feasibility of establishing an early warning signal using the increasing numbers of mild EV-71 cases and their lag time periods to appearance of severe EV-71 cases, and (3) to evaluate the trends of severe EV-71 cases over a 9.5-year period for providing better recommendations on public health efforts in the future
Age distribution of mild and severe EV cases Among the 1,517 severe EV cases notified to the TaiwanCDC during the study period, the mean age was 27 months [mean ± standard deviation (S.D.) = 27 ± 25.3], 61.4% were male, 71% were hospitalizations or referrals, and 12% were fatal

Summary

Introduction

Severe epidemics of enterovirus have occurred frequently in Malaysia, Singapore, Taiwan, Cambodia, and China, involving cases of pulmonary edema, hemorrhage and encephalitis, and an effective vaccine has not been available. The specific aim of this study was to understand the epidemiological characteristics of mild and severe enterovirus cases through integrated surveillance data. Severe epidemics of enterovirus have occurred frequently in Asia, including Malaysia [2], Singapore [3], Taiwan [4,5] and China [6]. The clinical severity varied from asymptomatic to mild symptoms [hand-foot-mouth disease (HFMD) and herpangina], severe pulmonary edema, hemorrhage and encephalitis [7]. Using an integrated surveillance system to monitor the enterovirus activity and fully understanding the difference in epidemiological characteristics between mild and severe enterovirus cases will be the most important prevention and control measures in public health

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